Various coffee decaffeination methods are known in the art. Coffee beans are first hydrated with water and then caffeine is extracted with liquid organic solvent such as benzene, ethyl acetate, isopropanol, chloroform, dichloroeythylene or trichloroethylene.
Various other methods are known which do not require the use of liquid organic solvents. In one such method supercritical carbon dioxide is used to extract caffeine from hydrated coffee. The coffee material so extracted may be in the form of premoistened raw coffee solids, either whole beans or particulate, or less preferably in the form of a liquid extract. Typically, caffeine is removed from the carbon dioxide so that the carbon dioxide can be recycled to the extraction process. U.S. Pat. No. 4,260,639 to Zosel discloses a carbon dioxide extraction process in which active carbon is used to remove the caffeine from the carbon dioxide. U.S. Pat. No. 4,411,923 to Hubert, et al. discloses a carbon dioxide extraction process in which ion exchange materials are used to remove caffeine from the carbon dioxide.
Supercritical carbon dioxide extraction process which use water to absorb caffeine from carbon dioxide are also known in the art. Some of these processed include removing caffeine from caffeine loaded water and reusing this water in the absorption process. U.S. Pat. No. 3,806,619 to Zosel discloses a process in which caffeine is separated from a wash water by air or nitrogen stripping. Water is stripped from caffeine loaded wash water and is then condensed and reused for caffeine absorption. U.S. Pat. No. 4,348,422 to Zosel discloses a process in which caffeine is separated from a wash water by distillation and the distilled water is then reused for caffeine absorption. Each of U.S. Pat. Nos. 4,341,804 and 4,246,291 to Prasad, et al. disclose a process in which evaporation, reverse osmosis or crystallization is used to separate caffeine from a wash water. A membrane permeate can be reused for caffeine absorption.